This invention relates to spreader rolls, in particular to a new and improved device of this general class which consists of a rigid, straight cylindrical sleeve rotatably mounted coaxially on a stationary supporting shaft, the sleeve surface being made up of a multitude of rigid cylinder elements which are movably connected to each other, to be used on machines for the manufacture of web materials such as paper, plastics, textiles, etc.
In the manufacture of paper, plastic, or textile material, the formation in the web of wrinkles or folds that run longitudinally in the direction of travel is an everpresent problem. They are caused by various forces acting upon the web while it is being processed. The forces originate form misalignments in the machinery, non-uniformities in the make-up of the web-material, or other process variations. Such wrinkles and folds in the processed webs will usually cause operational difficulties and quality deficiencies in the finished products. Therefore, special devices at regular intervals are required on web manufacturing machines to prevent or remove such wrinkles and folds. It follows that for better uniformity these devices are with very few exceptions made to constitute rotating rolls which support and effect the entire width of the webs.
Besides the prevention and elimination of wrinkles or folds in the web, the spreading forces exerted by the roll upon the web while it is being processed will in many cases result in improved physical properties of the web product. In particular the cross-machine tension forces put to a web while being processed will tend to equalize the physical properties present in the machine direction on the one hand and in the cross-machine direction on the other, resulting in an overall improvement of the web qualities. In paper, for instance, repeated cross-machine stretching during the drying phase will increase the cross-machine tensile strength substantially, to a value which can approach the otherwise highly accentuated machine-direction tensile-strength.
A spreader roll of the straight cylindrical type has been made known thru U.S. Pat. No. 3,344,493. This design embodies a rigid cylindrical sleeve rotatably mounted on a stationary shaft with the shell made up of a plurality of closely spaced and longitudinally arranged elastic bar elements.
This design of a straight cylindrical spreader roll when applied to wide webs has the disadvantage of producing a spreading action which is non-uniform over the width of the machine. This is caused by the friction forces generated between the sliding surfaces of elastic bars and supporting inner tube which is counter-acting the cyclical expansion/contraction movements of the bars. The restrictive friction-forces accumulate from the non-sliding mid-point of the roll length toward the roll ends and, therefore, result in a spreading action which is considerably greater on the roll edges than it is in the mid-section, where the spreading movements can come to a full stand-still under demanding conditions.
The present invention has as its objective to provide a marked improvement in the design of straight cylindrical spreader rolls.